陨石熔壳研究

A STUDY ON THE FUSION CRUST OF METEORITE

本文通过对毫县陨石熔壳的化学成分分析，Ｘ射线物相分析和红外光谱分析，并与陨石全岩相互对照，讨论了熔壳中Ｆｅ的氧化状态的变化、击变玻璃及主要矿物结构参数的变化；研究了熔壳的氧化作用、击变作用、击变作用下矿物的变形机制。同时，熔壳的ＳＥＭ显微形貌像给出了熔壳的一套完整剖面，从而讨论了熔壳的烧蚀作用主要有破碎作用、熔融作用和抽蚀作用三种方式。此外，透射电镜观察也证实了陨石熔壳中石英玻璃的存在。

n the present paper, the fusion crust of Boxian meteorite is analysed by several methods. Based on the chemical composition and compared with the whole meteorite. it can be found that the redox state of Fe in the fusion crust has changed: the amount of metal iron and FeS decreases, while that of Fe3+ increases, and new phases wustite and magnetite are formed.The phase analysis by X-ray powder diffraction shows that all the olivine in the fusion crust is forsterite compared to chrysolite in the internal meteorite because of phase transformation and phase rebuilding at high tempratures. In the meantime, the cell volume of the three dominant minerals in the fusion crust is larger than that inside the meteorite. The crystallographic parameters of all these three minerals decrease in one direction, and increase or keep constant in the other two directions. All these are concordant with one-direction stress. Due to the shock pressure, the minerals suffered one-dimensional crystal compression.The infrared spectrum pattern of the fusion crust reveals the occurrence of diaplectic glass,which indicates that the shock pressure is higher than 53. 0 GPa.The SEM micro-images of the fusion crust give a perfect section, which shows that the crust can be divided into three layers from the surface inwards: glassy layer, proous layer and transitional layer. The outer layer is made up entirely of glass. about 50Urn thick, and it is a real fusion crust. The mid-layer is porous, about Z10Um thick. The internal layer, about 250pm thick,is similar to that inside the meteorite except the grain sizes of the minerals.In these three layers, the grain size is of micrometer scale, unlike that in the internal meteorite. The absence of chondrules indicates that the fusion crust suffered breaking action under high shock pressure. The occurrence of the real fusion glass indicates that melting did take place in the fusion crust due to high temperature. The pores are formed due to extracting action.In summary, the fusion crust has been modified by the following processes: oxidation,shock, breaking, melting and extraction. All these results can give guides to the research of some aerospace materials.